Print NSData into Hex format

NSData+HexString.swift

//
//  NSData+HexString.swift
//  Cybertk
//
//  Created by Quanlong He on 8/14/15.
//  Copyright © 2015 Quanlong He. All rights reserved.
//

import Foundation

private let kHexChars = Array("0123456789ABCDEF".utf8) as [UInt8]

extension NSData {

    public func hexString() -> String {
        guard length > 0 else {
            return ""
        }

        let buffer = UnsafeBufferPointer<UInt8>(start: UnsafePointer(bytes), count: length)
        var output = [UInt8](count: length*2 + 1, repeatedValue: 0)
        var i: Int = 0
        for b in buffer {
            let h = Int((b & 0xf0) >> 4)
            let l = Int(b & 0x0f)
            output[i++] = kHexChars[h]
            output[i++] = kHexChars[l]
        }

        return String.fromCString(UnsafePointer(output))!
    }
}